Bleaching peroxide impregnated cellulosic fabrics by contact with a dry heated body



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AQUEOUS BLEACH AGENT (03-06%) BLEACHING STEP HEATED DRYING AT LEAST 90% ZONE AT OF WATER FROM |oo-|35c WATER WASH AQUEOUS FOR 20-90 BLEACHING soL. SECONDS ON CLOTH BLEACHED CELLULOSIC FABRIC FRANCIS XWMQY BERNARD K. EASTON BY NORBERT WElgBERG 7w & 7 z

Q iORNEYS May 9, 1961 F. x. NERNEY ETAL 2,983,568

BLEACHING PEROXIDEI IMPREGNATED CELLULOSIC FABRICS BY CONTACT WITH A DRY HEATED BODY Q Flled Aug. 1.8, 1958 2 Sheets-Sheet 2 mmtwei mmIm 3 mszmm mwhzuh m POI ENTORS FRANCIS X. NERNEY BERNARD K. EASTON NORBERT WEINBERG ORNEYS BLEACHING PEROXIDE IMPREGNATED CELLU- LOSIC FABRICS BY CONTACT WITH A DRY HEATED BODY Francis X. Nerney, Charlotte, N.C., and Bernard K. Easton, Williamsville, and Norbert Weinberg, Buffalo, N.Y., assignors to Food Machinery and Chemical Corporation, San Jose, Calif.

Filed Aug. 18, 1958, Ser. No. 755,430

Claims. (Cl. 8-111) This invention relates to the bleaching of cellulose fabrics, and particularly to the rapid bleaching of such fabrics.

Heretofore woven and nonwoven cellulose fabrics, for example those comprising fibers of cotton, jute, ramie and the like, have been bleached with peroxygen chemicals, employing mild temperature and chemical conditions which were thought necessary in order to avoid damage to the purified fibers used in their manufacture. For example, in the preferred process of treating the fabric in a J-box with active oxygen chemicals, see US. Patent No. 2,353,615, the fabric is contacted with active oxygen chemicals for from one hour to several hours with process heat being supplied by free steam. In this and other preferred prior art processes, the fibers which comprise the fabric are contacted only by dilute aqueous bleaching chemicals, and the temperature does not exceed about 100 C.

Attempts to reduce the bleaching time to less than about one hour have largely been unsuccessful, with the exception that a high pressure steam tecnique, see S.N. 640,085, filed February 14, 1957, in the names of two of the present inventors, Easton and Weinberg, has been developed. The method of this copending patent application, however, while it produces quality products in short times, requires special handling and the use of special equipment. For example, operation in accordance with the method of SN. 640,085 requires equipment which permits passage therethrough of fabric continuously while a steam pressure of from about 30-80 pounds per square inch is maintained in the equipment. Ac cordingly, it has been desired to provide a method where by purified cellulose fabrics can be bleached rapidly and in conventional bleaching equipment.

It is a feature of the present invention to provide a process of bleaching cellulose fabrics rapidly, and in standard fabric treating equipment.

It is a further feature of this invention to provide such a process operates without damaging the fibers which comprise the cellulose fabric.

In accordance with the method of the present invention, a cellulose fabric which has been desized and treated for mote removal is wetted thoroughly with an alkaline aqueous hydrogen peroxide solution, for example by immersing the fabric in the solution until a weight of solution about equal to that of the fabric is taken up by the fabric. The hydrogen peroxide solution employed contains about 1% to 1.75% of hydrogen peroxide, about 2% to 4% of a molecularly dehydrated salt of phosphoric acid, and about 0.3% to 0.6% of a suitable sequestering agent. The solution is employed at a pH of about 85-10.

The wetted fabric is heated to about 100 C. to 135 C. to evaporate water from the system rapidly and to concentrate on the fibers which comprise the fabric, hydrogen peroxide and other chemicals which are present in the saturating solution. This heating is continued until the fabric is at least about 90% free of water, which ice 2 normally takes about twenty to ninety seconds. Drying heat may be applied by passing the wet fabric over heated metal surfaces, preferably dry cans employed in textile drying equipment, or otherwise suitably by passing heated air through the fabric which is held in a drying tenterframe.

It is important that after the fabric is dried, it be washed with water tof ree it of residual chemicals, preferably within about three hours after drying. The washing operation in any event is not postponed for more than about sixteen hours after drying of the fabric, in order to avoid serious damage to the fibers.

It is surprising that the present bleaching operation, in which the fabric nned be contacted with an active oxygen formulation for only about 20 to seconds, provides increases in brightness in the fabrics comparable with the best results obtained with the previous long time, or high pressure, bleaching methods. It is even more surprising that this treatment of the pure cellulose fibers in cellulose fabrics, involving contact of the purified fibers with an alkaline peroxide solution which attains very high concentrations as the water in the system is driven off, is not accompanied by significant degradation of the fibers.

The following examples are presented as illustrative of the present invention, and are not intended to be limitative as regards reaction conditions or ingredients.

In these examples the cellulose fabric employed was a 2.1 yards per pound cotton fabric having a thread count of 124 x 64, and having a reflectance before bleaching of about 65%. The fabric samples were in the form of 40 inch wide strips. The fabric before bleaching was desized and treated for mote removal by a conventional enzyme and caustic method, wherein the fabric was first treated with an aqueous enzyme solution containing a detergent, and thereafter by boiling for 1 /2 hours in a 4% sodium hydroxide solution. Thereafter the goods were washed with water until the wash water had a pH of about 8.5, and bleached as described hereinafter in the examples.

Prior to bleaching the desized and caustic treated fabric had a reflectance of about 67.1%, and a fluidity (a measure of fiber strength) of about 2.4. Refiectances were determined with a Gardner Automatic Multi-purpose Reflectometer, manufactured by the Gardner Laboratory, Inc., of Bethesda, Maryland. Fluidities were determined by the A.S.T.M. Cuprammonium Method, D-539-53, and are stated as rhe units.

Example 1 An aqueous bleach bath was prepared which contained 30 g. of sodium hexametaphosphate, 5 g. of Sequestrene NA-4, 1.7 g. of sodium hydroxide, and 10 g. of hydrogen peroxide per liter. This solution had a pH of 8.5 Sequestrene NA-4, the tetrasodium salt of ethylene diamine tetracetic acid, is useful as a detergent and foam builder and as a polymerization activator. It is produced by the Alrose Division, Geigy Chemical Corp., 180 Mill Street, Cranston, Rhode Island.

The prepared fabric, see above, was impregnated with this bleach bath to provide on the fabric g. of solution per 100 g. of fabric. The impregnated fabric then was contacted for 20 seconds with the exterior polished surface of a stainless steel drum which was maintained at a temperature of about C. The temperature was maintained by providing steam within the drum at a pressure of about 3 pounds per square inch.

The impregnated fabric following this treatment contained less than 10% of saturant. Immediately after this heating operation the resulting fabric was washed free of residual chemicals with water, and dried. It was found to have a brightness of 78.7%, and a fluidity of 6.7,.

3 Example 2 An aqueous bleach bath was prepared which contained 30 g. of sodium tripolyphosphate, g. of Sequestrene NA-4, 1.7 g. of sodium hydroxide, and g. of hydrogen peroxide per liter. This solution had a pH of 10. The prepared fabric, see above, was impregnated with this bleach bath to provide on the fabric 80 g. of solution per 100 g. of fabric. The impregnated fabric then was contacted for 40 seconds with the exterior polished surface of a stainless steel drum which was maintained at a temperature of about 108 C. The temperature was maintained by providing steam within the drum at a pressure of about 6 pounds per square inch.

The impregnated fabric following this treatment contained less than 10% of saturant. Immediately after the heating operation the resulting fabric was washed free of residual chemicals with water, and dried. It was found to have a brightness of 86.8%, and a fluidity of 2.8.

Example 3 An aqueous bleach bath was prepared which contained 30 g. of tetrasodium pyrophosphate, 5 g. of Sequestrene NA-4, 1.7 g. of sodium hydroxide, and 17.5 g. of hydrogen peroxide per liter. This solution had a pH of 10. The prepared fabric, see above, was impregnated with this bleach bath to provide on the fabric 120 g. of solution per 100 g. of fabric. The impregnated fabric then was contacted for 40 seconds with the exterior polished surface of a stainless steel drum which was maintained at a temperature of about 110 C. The temperature was maintained by providing steam within the drum at a pressure of about 7 pounds per square inch.

The impregnated fabric following this treatment contained less than 10% of saturant. One hour after the heating operation the resulting fabric was washed free of residual chemicals with water, and dried. It was found to have a brightness of 87.3, and a fluidity of 3.0.

Example 4 An aqueous bleach bath was prepared which contained 30 g. of tetrasodium pyrophosphate, 5 g. of Sequestrene NA-4, 1.7 g. of sodium hydroxide, 5 g. of borax, and 17.5 g. of hydrogen peroxide per liter. This solution had a pH of 10. The prepared fabric, see above, was impregnated with this bleach bath to provide on the fabric 100 g. of solution per 100 g. of fabric. The impregnated fabric then was contacted for 40 seconds with the exterior polished surface of a stainless steel drum which was maintained at a temperature of about 108 C. The temperature was maintained providing steam within the drum at a pressure of about 6 pounds per square inch.

The impregnated fabric following this treatment contained less than 10% of saturant. Two hours after this heating operation the resulting fabric was washed free of residual chemicals with water, and dried. It was found to have a brightness of 87%, and a fluidity of 4.

Example 5 A bleach bath was prepared which contained 30 g. of sodium tripolyphosphate, 5 g. of Sequentrene NA-4, and 17 g. of hydrogen peroxide per liter. This solution had a pH of 9.1. The prepared fabric, see above, was impregnated with this bleach bath to provide on the fabric 100 g. of solution per 100 g. of fabric. The impregnated fabric then was contacted for 1 minute with the exterior polished surface of a stainless steel drum which is maintained at a temperature of about 108 C. The temperature was maintained by providing steam within the drum at a presure of about 6 pounds per square inch.

The impregnated fabric following this treatment contained less than 10% of saturant. Eight hours after this heating operation the resulting fabric was washed free of residual chemicals with water, and dried. It was found to have a brightness of 81%, and a fluidity of 8.6.

4 Example 6 An aqueous bleach bath was prepared which contained 30 g. of sodium tripolyphosphate, 5 g. of Sequestrene NA-4, 5 g. of borax, 1.8 g. of sodium hydroxide, and 17 g. of hydrogen peroxide per liter. This solution had a pH of 9.5. The prepared fabric, see above, was impregnated with this bleach bath to provide on the fabric 100 g. of solution per 100 g. of fabric. The impregnated fabric then was contacted for 40 seconds with the exterior polished surface of a stainless steel drum which was maintained at a temperature of about 115 C. The temperature was maintained by providing steam within the drum at a pressure of about 10 pounds per square inch.

The impregnated fabric following this treatment contained less than 10% of saturant. Immediately after the heating operation the resulting fabric was washed free of residual chemicals with water, and dried. It was found to have a brightness of 81.2%, and a fluidity of 2.8. The fabric was tested further for tensile strength, in accordance with the A.S.T.M. Test Method 5100, of May 15, 1951. A sample of the unbleached fabric had a warp break strength of 197.5 pounds, and a fill break strength of 103.5 pounds. The bleached fabric had a warp break strength of 192.5 pounds, and a fill break strength of 116.5 pounds.

Example 7 The bleach bath of Example 6 was used to impregnate a prepared fabric, see above, to provide on the fabric 100 g. of solution per 100 g. of fabric. The impregnated fabric then was contacted for 20 seconds with the exterior polished surface of a stainless steel drum which was maintained at a temperature of about 135 C. The temperature was maintained by providing steam within the drum at a pressure of 31 pounds per square inch.

The impregnated fabric following this treatment contained less than 10% of saturant. Immediately after the heating operation the resulting fabric was washed free of residual chemicals with water, and dried. It was found to have a brightness of 79.4%, and a fluidity of 3.4.

Example 8 The bleach bath of Example 6 was used to impregnate a prepared fabric, see above, to provide on the fabric g. of solution per 100 g. of fabric. The impregnated fabric then was contacted for seconds with the exterior polished surface of a stainless steel drum which was maintained at a temperature of about 110 C., the temperature being maintained by providing steam within the drum at a pressure of about 6 pounds per square inch.

The impregnated fabric after this treatment contained less than 10% of saturant. Immediately after this heating operation the resulting fabric was washed free of residual chemicals with water, and dried. It was found to have a reflectance of 81.7, and a fluidity of 3.6.

Example 9 The bleach bath of Example 6 was used to impregnate a prepared fabric, see above, to provide on the fabric g. of solution per 100 g. of fabric. The impregnated fabric then was contacted for 20 seconds with the exterior polished surface of a stainless steel drum which was maintained at a temperature of about 108 C. The temperature was maintained by providing steam within the drum at a pressure of 6 pounds per square inch.

The impregnated fabric following this treatment maintained less than 10% of saturant. Sixteen hours after the heating operation the resulting fabric was washed free of residual chemicals with water and dried. It was found to have a fluidity of 10.5, and a brightness of 85.4%.

The cellulose fabrics to be treated according to the method of the present invention are those woven and nonwoven fabrics prepared from cellulose fibers, for example cotton fibers, jute fibers, or ramie fibers. These fibers before their use in fabrics are chemically purified by reaeeases moval of lignin and other noncellulosic material, and frequently they are sized, that is treated with such agents as starch, resins, and the like, to enhance their appearance and feel. A flow plan of the invention is shown in the attached drawings.

In the drawings:

Figure 1 represents a flow sheet of the process, in block form, to represent the chemical and physical treating operations hereinafter described.

Figures 2 and 3 represent flow diagrams showing the manipulative operation of the process; Figure 2 shows one embodiment of the heating and drying zone in which heating cans are employed, whereas Figure 3 shows a heating and drying zone employing a tenterframe and hot air.

Preliminary to operation according to the present process, and where the purified cellulose fabric bears a sizing agent it may be given a standard prepare, that is it may be treated with an aqueous enzyme solution and then with an alkaline aqueous solution to remove this sizing agent and motes which may be present. Following treatment of the cellulose fabric with the strongly alkaline solution, and prior to bleaching as described herein, the fabric is washed with water to remove excess alkali. Completion of the washing operation can be determined by measuring the pH of the wash water as it is removed from the fabric, and is reached when thepH of this wash water is no more than about 8 to 9. In the event the fabric has not been given a sizing treatment, it will be apparent that such a pretreatment before bleaching will not be necessary.

The cellulose fabric then is bleached. In accordance with the present process, it is first contacted with an aqueous solution containing about 1% to 1.75% of hydrogen peroxide, calculated as 100% H 0 This reagent preferably is introduced as 35% aqueous hydrogen peroxide, although as is well known it may be employed in lesser or greater concentrations, and likewise may be introduced in the form of Na 0 provided the H 0, concentration in the bleach solution be about 1% to 1.75

The peroxide solution also contains about 2 to 4% of a molecularly dehydrated salt of phosphoric acid, typically sodium tripolyphosphate, sodium hexametaphosphate, or tetrasodium pyrophosphate, and a sequestering agent, for example about 0.3 to 0.6% of an ethylene diamine tetracetic acid sequestrant, a sodium salt of this acid, or a sodium salt of pentaacetic acid.

Where necessary the solution thereafter is adjusted to a pH of about 8.5 to 10.0 with a strong alkali, for example sodium hydroxide or potassium hydroxide. It frequently is desirable also to include in the formulation 9. buffer which will maintain the pH of the solution during the operation at the desired level of about 8.5 to 10, and where this is desired about 0.4 to 0.6% of borax or other boric acid derivative has been found suitable.

The prepared cellulose fabric is substantially saturated with the aqueous hydrogen peroxide solution, that is it is impregnated with about 80-120% of its own weight of the solution. Thereafter the wetted cellulose fabric is heated to drive ofi water in the impregnant solution. The heating may be effected suitably at about 100-135 C., for example by contact of the fabric with a heated metal surface, such as that of a drying can of the type commonly employed in textile mills, by passing heated air through the fabric which is stretched on tenter-frames, or by other suitable means. The heating conditions are such that the fabric is essentially dried, that is at least about 90% of the water added to the fabric in the saturating solution, is removed, in from about 20 to 90 seconds.

Within about sixteen, and preferably within about eight hours, after this drying operation the cellulose fabric is washed with water to remove residual chemicals which remain therein after this removal of water. The

washing can be carried out at any time up to about sixteen hours after the drying operation, with increasing but not severe damage to the fabric. However, permitting the fabric to stand for substantially beyond this period without washing causes severe degradation of the constituent fibers which comprise the fabric.

The washing preferably comprises rinsing the fabric in water although subjecting the treated, unwashed fabric to another wet treatment which will remove the residual chemicals has been found satisfactory. An example of such a wet treatment is caustic mercerization, where the fabric is treated with caustic and thereafter immediately water washed. In any event no more than about sixteen hours should elapse before washing with water.

As an illustration of the effectiveness of the present method, the reflectance of a typical cotton fabric before the above bleaching treatment is about 62% to 67% as measured with a Gardner Automatic Multi-purpose Reflectometer. Following bleaching of the fabric according to the above process, the brightness of the bleached cotton fabric is raised to about 75% to No substantial degradation of the fibers occurs as a result of operation according to this process. One standard test for determining degradation of cellulose fibers is to dissolve the fibers in a cuprammonium solution, and to measure the fluidity of the resulting solution. Fabrics having fluidities of about 10 or less are generally considered in the art to be suitable. As indicated in the above examples, the fluidities of cuprammonium solutions of the herein bleached fibers are substantially below this value of 10, and inmost cases are essentially the same as the fluidity of the corresponding solution of an unbleached cellulose fiber. Further, as shown in Example 6, the tensile strength of the fabric is not lessened by the present treatment. Thus, the marked improvement in brightness of the present fabrics is obtained without noticeable degradation of their constituent fibers.

Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplified in a manner so that it can be readily practiced by those skilled in the art, such exemplification including what is considered to represent the best embodiment of the invention. However, it should be clearly understood that, within the scope of the appended claims, the invention may be practiced by those skilled in the art, and having the benefit of this disclosure, otherwise than as specifically described and exemplified herein.

What is claimed is:

1. Method of bleaching a cellulose fabric, comprising impregnating said fabric with an aqueous hydrogen peroxide solution having a pH of about 8.5 to 10 and containing by weight about 1% to 1.75% of hydrogen peroxide, about 2 to 4% of a molecularly dehydrated salt of phosphoric acid, and about 0.3 to 0.6% ,of a sequestering agent, whereby said fabric takes up about 80 to 120% of its own weight of said solution, dry heat ing the resulting wetted fabric by contact with a heated body to about C. to 135 C. for about 20 to 90 seconds to remove at least about 90% of the water present on said wetted fabric, and within about sixteen hours after said heating has been completed, washing residual chemicals out of said fabric.

2. Method of bleaching a cellulose fabric, comprising impregnating said fabric with an aqueous hydrogen peroxide solution having a pH of about 8.5 to 10 and containing by weight about 1% to 1.75% of hydrogen peroxide, about 2 to 4% of a molecularly dehydrated salt of phosphoric acid, from the group consisting of sodium tripolyphosphate, sodium hexametaphosphate, and tetrasodium pyrophosphate, and about 0.3 to 0.6% of a sequestering agent, whereby said fabric takes up about 80 to of its own weight of said solution, heating the resulting wetted fabric by contact with a heated drying surface to about 100 C. to C. for about 20 to 90 seconds to remove at least about 90% of the. water 2,988,568 7 8 present on said wetted fabric, and within about 16 hydrated salt of phosphoric acid is tetrasodium pyrohours after said heating has been completed, washing phosphate. residual chemicals out of said fabric with water.

3. Method of claim 2, wherein the molecularly de- S Cited i the file Of this patent hydrated salt of phosphoric acid is sodium tripolyphos- 6 UNITED STATES PATENTS phate.

4. Method of claim 2, wherein the molecularly de- 2,740,689 Easton et a1. Apr. 3, 1956 hydrated salt of phosphoric acid is sodium hexameta- 2,839,353 Coleman June 17, 1958 phosphate. 2,893,819 Hawkinson July 7, 1959 5. Method of claim 2, wherein the molecularly de- 10 

2. METHOD OF BLEACHING A CELLULOSE FABRIC, COMPRISING IMPREGNATING SAID FABRIC WITH AN AQUEOUS HYDROGEN PEROXIDE SOLUTION HAVING A PH OF ABOUT 8.5 TO 10 AND CONTAINING BY WEIGHT ABOUT 1% TO 1.75% OF HYDROGEN PEROXIDE, ABOUT 2 TO 4% OF A MOLECULARLY DEHYDRATED SALT OF PHOSPHORIC ACID, FROM THE GROUP CONSISTING OF SODIUM TRIPOLYPHOSPHATE, SODIUM HEXAMETAPHOSPHATE, AND TETRASODIUM PYROPHOSPHATE, AND ABOUT 0.3 TO 0.6% OF A SEQUESTERING AGENT, WHEREBY SAID FABRIC TAKES UP ABOUT 80 TO 120% OF ITS OWN WEIGHT OF SAID SOLUTION HEATING THE RESULTING WETTED FABRIC BY CONTACT WITH A HEATED DRYING SURFACE TO ABOUT 100*C. TO 135*C. FOR ABOUT 20 TO 90 SECONDS TO REMOVE AT LEAST ABOUT 90% OF THE WATER PRESENT ON SAID WETTED FABRIC, AND WITHIN ABOUT 16 HOURS AFTER SAID HEATING HAS BEEN COMPLETED, WASHING RESIDUAL CHEMICALS OUT OF SAID FABRIC WITH WATER. 